linux-kernel - Re: [Qemu-devel] [RFC qemu 0/4] A PV solution for live migration optimization

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Date:	Fri, 4 Mar 2016 11:47:09 +0200
From:	"Michael S. Tsirkin" <mst@...hat.com>
To:	"Li, Liang Z" <liang.z.li@...el.com>
Cc:	"Dr. David Alan Gilbert" <dgilbert@...hat.com>,
	Roman Kagan <rkagan@...tuozzo.com>,
	"ehabkost@...hat.com" <ehabkost@...hat.com>,
	"kvm@...r.kernel.org" <kvm@...r.kernel.org>,
	"quintela@...hat.com" <quintela@...hat.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"qemu-devel@...gnu.org" <qemu-devel@...gnu.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"amit.shah@...hat.com" <amit.shah@...hat.com>,
	"pbonzini@...hat.com" <pbonzini@...hat.com>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	"virtualization@...ts.linux-foundation.org" 
	<virtualization@...ts.linux-foundation.org>,
	"rth@...ddle.net" <rth@...ddle.net>
Subject: Re: [Qemu-devel] [RFC qemu 0/4] A PV solution for live migration
 optimization

On Fri, Mar 04, 2016 at 09:12:12AM +0000, Li, Liang Z wrote:
> > Although I wonder which is cheaper; that would be fairly expensive for the
> > guest wouldn't it? And you'd somehow have to kick the guest before
> > migration to do the ballooning - and how long would you wait for it to finish?
> 
> About 5 seconds for an 8G guest, balloon to 1G. Get the free pages bitmap take about 20ms
> for an 8G idle guest.
> 
> Liang

Where is the time spent though? allocating within guest?
Or passing the info to host?
If the former, we can use existing inflate/deflate vqs:
Have guest put each free page on inflate vq, then on deflate vq.

-- 
MST